//编写一个程序，通过填充空格来解决数独问题。 
//
// 数独的解法需 遵循如下规则： 
//
// 
// 数字 1-9 在每一行只能出现一次。 
// 数字 1-9 在每一列只能出现一次。 
// 数字 1-9 在每一个以粗实线分隔的 3x3 宫内只能出现一次。（请参考示例图） 
// 
//
// 数独部分空格内已填入了数字，空白格用 '.' 表示。 
//
// 
//
// 
// 
// 
// 示例 1： 
//
// 
//输入：board = [["5","3",".",".","7",".",".",".","."],["6",".",".","1","9","5",".
//",".","."],[".","9","8",".",".",".",".","6","."],["8",".",".",".","6",".",".",".
//","3"],["4",".",".","8",".","3",".",".","1"],["7",".",".",".","2",".",".",".","6
//"],[".","6",".",".",".",".","2","8","."],[".",".",".","4","1","9",".",".","5"],[
//".",".",".",".","8",".",".","7","9"]]
//输出：[["5","3","4","6","7","8","9","1","2"],["6","7","2","1","9","5","3","4","8
//"],["1","9","8","3","4","2","5","6","7"],["8","5","9","7","6","1","4","2","3"],[
//"4","2","6","8","5","3","7","9","1"],["7","1","3","9","2","4","8","5","6"],["9",
//"6","1","5","3","7","2","8","4"],["2","8","7","4","1","9","6","3","5"],["3","4",
//"5","2","8","6","1","7","9"]]
//解释：输入的数独如上图所示，唯一有效的解决方案如下所示：
//
//
// 
//
// 
//
// 提示： 
//
// 
// board.length == 9 
// board[i].length == 9 
// board[i][j] 是一位数字或者 '.' 
// 题目数据 保证 输入数独仅有一个解 
// 
// 
// 
// 
// Related Topics 数组 回溯 矩阵 👍 1261 👎 0

package leetcode.editor.cn;
//leetcode submit region begin(Prohibit modification and deletion)
class Solution37 {
    public void solveSudoku(char[][] board) {
        backTracking(board);
    }

    public boolean backTracking(char[][] board){
        for(int i = 0; i < board.length; i++){
            for(int j = 0; j < board[0].length; j++){
                if(board[i][j] != '.') continue;
                //字符0-9的ascii为48-57
                for(char k = '1'; k <= '9'; k++){ //char可以直接比大小
                    if(valid(i, j, k, board)){
                        board[i][j] = k;
                        //找到一组合适的立刻返回
                       if(backTracking(board)) return true;
                        board[i][j] = '.';
                    }
                }
                return false;
            }
        }
        return true;
    }

    private boolean valid(int row, int col, char k, char[][] board) {
        //检查同行上是否有重复元素
        for(int i = 0; i < board.length; i++){
            if(board[row][i] == k){
                return false;
            }
        }
        //检查同列上是否有重复元素
        for (char[] chars : board) {
            if (chars[col] == k) {
                return false;
            }
        }
        //检查同一方格内是否有重复元素
        int startRow = (row / 3) * 3;
        int startCol = (col / 3) * 3;
        for(int i = startRow; i < startRow+3; i++){
            for(int j = startCol; j < startCol+3; j++){
                if(board[i][j] == k){
                    return false;
                }
            }
        }
        return true;
    }

    public static void main(String[] args) {
        //字符0-9的ascii为48-57
        System.out.println('1');
        System.out.println('1'+1);
    }
}
//leetcode submit region end(Prohibit modification and deletion)
